Solvent extraction process



NOV. 22, 1955 R. A. FINDLAY SOLVENT EXTRACTION PROCESS Filed Sept. 24. 1951 INVENTUR. R A FINDLAY TTORNEVS ation.

SOLVENT EXTRACTION PROCESS Robert A. Findlay, Bartlesville, Okla., assignor to Phillips i Petroleum Company, a corporation of Delaware Application September 24, 1951, Serial No. 247,967 13` Claims. (Cl. 260-666) This invention relates to a solvent extraction operation. In one aspect it relates to a method for the production of reflux for reiluxing a solvent extraction oper- In another aspect it relates to a method for` the production of liquid reux material for use in solvent extraction operation wherein the extract phase distillation load is minimizedr` In solvent extraction operations wherein liquid` retlux is produced and introduced into the extration zone this reux is ordinarily a portion of the extract material product stream.` In this type of operation all of the extract phase is distilled for the recovery of the solvent for recycling purposes andfor the production `of the extract product. While it is `conventional to use `a portion of the actual extract material as reliux it is not necessary to employ a material entirely free from solventfor refluxing purposes, such as` that produced by distillation. The volume of extract phase is ordinarily relatively large since in usual operationsthe ratio of solvent to extract materials is quite large and considerable amounts of heat have to be utilized in `separation ot"` the solvent from the extract. It is considered advantageousto use some intermediate product of substantial purity for reiiuxing purposes in place of the fully purified `extract product. If such a material is available in an extraction operation the cost of extract phase distillation is materially reduced because of the reduced heat load required for distilling smaller volumes of extract phase.

One object of my invention is to provide an improved solvent extraction process.

Another object of my invention is to provide a process for the production of reiiux material for use in an extraction operation.

Another object of my invention is to provide a process for the production of a reux `material from a less expensive operation than that usually employed.

Still another object of my invention `is to devise a` process for the production of a reliuxqmaterial sutii- `ciently pure for extraction tower `refluxing purposes without utilizing an extract still for its production.

Still other objects and advantages of my process will berealized upon reading the following disclosure which taken with the attached drawing forms a `part of this specication. i i

The drawing represents diagrammatically one form of apparatus suitable for carrying out the process of my invention. p

Referring `now to the drawing, reference numeral 12 identifies a liquid-liquid `extract column of conventional design. This extract column may be packed with any desired type of liquid-liquid contact promoting apparatus providing it promotes satisfactory `contacting of the A charge stock feed line 11 is provided at about a mid-point of the tower.

Line 13 is for `withdrawal of raffinate phase and passagel to a rainate phase distillation still 17. This still isprovided with an overhead vapor withdrawal line 18 which contains condenser `19. Conduit 21 carries condensate 2,724,731 Patented Nov. 22, 1955 ICC` from condenser 19 to an accumulator 22. Line 20 is for raffinate product removal While a line 23 is for return of a portion of the condensate to the still 17 as reflux. Still 17 is provided with a reboiler coil 24 and a bottoms drawot line 25. A run tank 26 provided with a pressure relief line 27 is intended to serve as a run storage for solvent in the process. A line 14 leads from the bottom of this run tank 26 to the upper portion of the extract column 12 'for introduction of solvent` to the operation. A line 16 positioned at a point near the bottom of the vessel 12 is for introduction of liquid reflux produced according to my invention. A line 15 is provided at the bottom of the vessel 12 for withdrawal of extract phase. A heat exchanger 29 is provided for cooling material owing from line 15 by material from a line 49. Cooled material from this exchanger flows on through a line 30 into a cooler or chiller 31. From this chiller material passes by way of,` a conduit 38 into a crystal purifier 39. This chiller 31 is actually considerably more than a mere cooling means, since itis provided with a piston 35 for transferring solid material produced in cooler 31 and remaining liquid material through line 38 into the purifier 39. Coolant for carrying out a crystallization operation in cooler 31 enters this apparatus through an inlet line 36 and exits therefrom by way of an outlet line 37.

To the piston 35 is attached a piston rod 34 which is pivoted to a pitman 33 which in turn is powered by a source of power 32. The pitman is pivoted by element 66 to the source of power 32 and by rotation of element 32 the piston 35 reciprocates'to advancesolid and liquid material in conduit 38 and to draw liquid material to be cooled in cooler 31 from line 30.

The crystal purifier 39 is provided with a heating coil 40 at a point near its bottom and a reciprocating porous piston 41` as illustrated. This reciprocating `porous piston is attached to a piston rod 42 which in turn is powered by an apparatus 43 which contains a piston, not shown. This piston in power element 43 is reciprocated by the `introduction of air pressure alternately through lines 45 and 46. In the operation of this power element 43, when air pressure is admitted thereto through line 45 the piston 41 is forced downward with air exhausting through line 46. In like manner when air pressure is admitted through line 46 the piston rises and air is exhausted through line 45. Attached to the bottom of the crystal puritier 39 is a `line 65 for passage of material from the bottom of this separator by way of a line 28 into the run tank 26. To the top of this phase separator 39 is attached a line 47 for transfer of liquid to a liquid phase separator 48. The line 49 is connected to the top of this liquid phase separator and to the heat exchanger 29. Material passing from the separator 48 through line 49 passes throughthe tubes of the exchanger 29 and through line 16 into the lower portion of the extractor 12. A line 50 connected with the bottom of the liquid phase separator 48 is intended to conduct liquid therefrom to a heat exchanger 51 from which a line 52 extends on to a still 53. This still is provided with an overhead vapor withdrawal line 54 which is provided with a condenser 55. A line 56 leads from the condenser for passage of condensate, a portion of which is passed through a line 57 into the still 53 as reflux and the remaining portionpasses through a line 58 into an accumulator tank 59. This accumulator tank 59 also serves as a phase separator in which an extract product phase separates and is removed through a line 60 while material for recycling in the process is removed through lines 61 and67 into the heat exchanger 51. ln this line 67 the material from line 61 is mixed with the material from still 53 passing through line 63. This combined material is cooled somewhat in the exchanger 51 and this plsd. wmbinsd material, passes.

oii'ilirughwamlire'6iwwithmniaterial added from the line 65 and the mixture is passed on through line 28 into the Illu, taak 2.6- 'Ihs still-5.3 .is provided with a reboiler cgil 62 for .Saprlying kreation distillation.

T13@ aborti mentioned ,Crystal purier 39, as applied i0 one step of .my process, is yfully! described. in a copending application hyv John A.. Weedman, Serial No. 166,992,`

sii-9. 195.0..

l.. wille xplain the operation of thisy apparatus using as an examplethe separation of'rnethylcyclohexane from adnliixture with :1 -heptane by a solvent Consistingsubstantially1 of aqu ous phenol, inv which operation somev relatively ptlre, r r1 ethyrlcyclohexane as an intermediate product is produucelandreycled.into the extraction operation for rreuiflurringl the .Y extract1 column, In this operatiom to each, ltmpparttsv by weight ofi charge stock containing equal parts-by weight of n-heptane and methylcyclohexane is addedahout 18(1)()E partsvby weight of wet phenol. This wet orwater-:containingphenol Imay contain as much as from 5 to 15I per cent by weightkof water, preferably ahout per cent. The liquid-liquid extracting operation carried out in, therextract vessel -12 may be carried olut.hetweenl the temperatures vof about 70 and 150 F., preferahlybetween 125 and f130 F, Under thesetemperature andy solvent to feed ratio conditions, there is produeda raii'inateYphase,` containing substantially all of the n-hep't/anei. This! raffinate phase is withdrawn through the raftinatewithdrawal lin e' 13. From this raffinate phase is separatei,U in, the raffinatek still 17 phenol containing `rrisvxisture as stillV bottoms74 while the. nfheptane passes'overhead throughthe vapor line 18. This vaporis condensed in condensery 1 9 and condensatel passes through line 21 into accumulator 22. From this accumulator a portion: l of the` condensate is withdrawn through line 23| and reintroducedy into still 17 for refluxing purposes, while thatcondensate not needed for reuxing is'withdrawn through the product lne20 and passed tostorage or `other disposal, notlshown.` This material passing1 through linepztlrcontains substantially the entireA SOpoundsby weight Qin-heptane of, about 95 per cent purity! VThe extract phase from the extractor 12is removed. through theexutractl line 175,. and iswcooled in the heat exchangerL 29., This cooled extract phase is passed,l on

through the line, into the chillery 31- in which the ex-` tract phase iscooled to Va temperatureof from about tow F. At this temperature a considerable portion of ltlviewphenolgsfmarates as rsolidtcrystals of phenol. Sui- Ciantof. the .Phenpifcrystallizes to iform a slurry high in. solidscontent, andthis.A slurry is transferred by the ref ciproetingpiston `35,.:into the crystal purier39by way ofthe conduitV 38,. Cooling, medium for this crystalliza-y tionwoperation is admitted'to: the chiller 31 through line 3@ d. is Withdrawn ibersfrln byway 0f line 37-` The.y pi 345; is*rleciproncatedV bythe power means 32 as expla ed hercinbafra The' crystal purifier 3,9 isuoperated inV such a manner thatthe methylcyclohexanephase separated in cooler 31, along with somelliquid phenol containing dissolved water and saturated with. methylcyclohexane are withdrawn throughlhe linei47 into the phase `separator 48. The

crystals of phenol entering theseparator` 39 are compressed and forceddownwarddby each downward movement of the porollspiston 41 in sucha manner that liquid belowi the massief crystals tends `to riseupward through a mass of crystals, si nce the piston 41is porousandrper mit sliquid,-.ow therethrough;l Atthesametime some heat Visv providelsby the heatingcoil 40 to melt thelcrysy talsof phenol reaching the region of the heating coil. A portion .of .this melted phenol flowsthrough pipe 65 in the direction of pipe 28 and run tank 26 while some of the melted phenol owsupward through the bed lof the remaining phenol crystals'asthe piston 41 is moved down ward; 'tnuring'iniervn's in which nie piston is moving upward. soms. additional charge. stock is introduced into the separator 39 by the action of the reciprocating piston 35. Then upon addition of such an amount of charge material the piston 41 moves downward to compress the crystals and force some of the liquid phase upward between the crystals and through the piston and some of the melted phenol through tlieline 65. In this manner only melted phenol is passed through line 65 while substantially all of Athe waterin solution in the phenol-rich liquid phase inlthe` upper portion` of purifier 39, alongA with the methylcyclo'hexane-rich phase are removed through the linel4`7. When these two liquid phases*l enter separator' tank 48 they separate according toA the specifc gravities. Thek me'thylc'yclohexanefphase of course is the lighter phase and it iloats on the surface of the relatively heavy phenol-rich phase. As mentioned hereinbefore, this phenol-rich phase is substantially a saturated solution ofmethylcyclohexane in phenol, which solution also contains substantially all oftheiwatencontentleaving4 the. puriiier .vessel 39. Thisy phenol-rich` phase .then leaves this separatorthrough the .line 50 andis warmed in the exchanger. 51 and. isfinalliy passed throughline 52.-.into, the. still 53,. This..sti1l 53. isfthe extract productstill,v which only a relatively small volumeot material"y is chargedffor. dist-illationiY Since waters-and.I methylcyclohexane. boil at very nearlyl the, same7 temperaturel these two materialspass overhead from still.53 asL vapor through the line 54. This mixed. vapor is` condensed in the. condenser.. 55- and, condensatepasses,throughthe line 56, a portion beingxetttrned-i as reux to :the still throughthe lineS-'lf-and the remainder-beingrpassed throughline 58: into the separator..tank.59. In this.tanktheimethylcyclohevane floats `upon :.thesurfaceofgthe condensedwater, the former .being removed. atf product liuettlt while the` water ispassed. through. the line.61 to be..combinediwith the bottoms from .the still 53u 'Ihebottomsfrom thestill. 53 is substantillypure phenol and;the.mixture.of1phe nol` from :line '.63 and .'water. fromline, 61 is .passed-through: the line .67,1 is cooled inthe exchanger 51. andzpassedon through the.line2.64. Phenol fromthe. purifier-.39: is .added` through line. 65; and. the; mixture -passe'd .throughv` line-28. into therun storage. tank. 26. Material .enterng the runl storage .tankl 26-y vthrough iline 25 i andline 28 imake/ up fthe. solvent. ofi desiredI composition. for use. in the. solvent 'extraction operation.: While thevalved aline; 27 may be.used. for. pressuref reduction. purposes; in. case pressure reduction is necessary, this line may also-be used .forintroduction of -:makeip .waterwhen neededand for-,theintroduction of phenoleasneededt; A.valvedline. 44 is.attacl:1ed: to line 61 as shown for removal of water from thesolvent.` systemias needed.` i

Inzthe operation oftheheating coili40 .inthe-bottom of. the purifier vessel 39; suiicientiteinperature is. maintainedk by coil -40 .to melttthe-phenol crystals and heat `the liquid leaving. thisv .vessel.l through. line 65 ato a .temperature `off aboutltl() to. 1159; In normal,operationsbasediupon the 1800..par`ts:byzweightfuwet phenol per..100=parts.by. weighttof -charge stock;J charged tothe.. extraction. operation,`. there .is .meltediby..the hetingcoil'AOtmore `than.70,0 f toSOO .partsh'by weight oflphenolt. 1 This;.700:.to.800 parts; by weight of phenol is passed through line 65.-infoline.:

28., while the excessmelted.phenollpasseszllpwardithrough the' bed L oftfphenol; :crystals as; the porous.:pistonV 41;.; is. moved downward. This portion of the melted phenol; whichpasses upward:through-themed,Ofsphenolgcrystals washes, the.crystals,below the, 4point -ofr .-feedinlet,I sov that the `material fleavinghvessel 39.;throughgline (65 iwilllrcovxietainsubstantially.nonnethylcyclo ,exane ras 1a separate iliqi, uid. phase.. ,1y And further, this.meltellPhs111401 inlnt65will contain substantiallynnog. methyloyclohexane inlizsolution. sincev this. phenol. originates entirely. onsubstantially. frommelting phenolcrystals.

Since thephenol passing throughlinel is substantially pure. -phenolpk landether.phenoL-.passinggfthrough line, 6SM-is still-bttoms, and: the watertpassingxt throught line... 6L

solvent mixture useful in my process.

contains no hydrocarbon infsolution, all of the recycled solvent components entering the run storage tank 26 are free `from extract product and accordingly, no extract material is introduced with the extractant through line 14. In this manner the raffinate phase withdrawn through line 13 is maintained in a relative pure condition, free from contamination with extract material. The relatively small amount of phenol separated in the raiiinate still 17 isusually free from extract material since it results from the distillation of the rainate phase.

Thekettle section of the still 53 is maintained at a temperature of from 360 to 375 F. by the addition of heat from the reboiler coil 62. In this manner the still bottoms are substantially pure phenol, while all other materials, that is,` water and methylcyclohexane, are easily driven overhead.

t Based upon the above mentioned amounts of charge stock and solvent charged to the extractor 12, the phenolrich phase removed from the separator 48 and introduced into the still 53 consists of about 1000 parts by weight of phenol and water, and the 50 parts by weight of methylcyclohexane. By the removal of from 700 to 800 parts by weight of substantially pure phenol from the bottom of the puriier 39, which 700 to 800 parts by weight is nearly one-half of the phenol charged to the extractor 12, about one-half of the heat load requirement is saved in the operation of the extract recovery still 53.

This method of producing reux material produces about 350 parts by weight of relatively pure methylcyclohexane in the phase separator 48, which reflux material is passed through the line 49, the heat exchanger 29, and on through line 16 to retlux the extract end of the extractor.

Wet phenol works exceptionally well according to the process of my invention, since the temperature in the crystallizer 31 needs to be only from 35 to 40 F. The maintenance of such a temperature is relatively inexpensive and is preferable to supplying additional heat for distillation in the extract recovery still 53.

The water and phenol mixture passing through line 67 contains about 18 per cent water based on the over-all l per cent water in the solvent entering the extractor 12.

While I have explained the operation of my process `using wet phenol as the extraction solvent, other materials can be used as extractants. For example, o-cresol containing water in solution, p-cresol containing water in solution, xylenol (2,3-di-methylphenol) with water in solution, as well as levulinic acid containing water in solution may be used as extraction solvents.

When using these other materials as extraction solvents, the temperatures of crystallization in the crystallizer 31 will need to be somewhat different, dependent somewhat upon the melting point of the organic compound and upon its water content, and also upon the concentration of the extracted material in the solvent. While the above mentioned compounds are enumerated as useful in my process, mixtures of these materials may also be used, but it is preferable to use the individual compounds. A mixture of o-cresol and p-cresol serves as an example of a In like manner, such a material as phenyl phthalate in which water is not soluble may be used in the process of my invention. Phenyl phthalate melts at about 69 to 70 C. This material exhibits a miscibility temperature with n-heptane of 135 C., with l-heptene of 79 C. and with cyclohexane of 41 C. Thus based on these miscibility ternperatures, phenyl phthalate may be used in my process as an extraction solvent. When treating a mixture of these hydrocarbons at a temperature below 135 C. and above 79 C. l-heptene and cyclohexane are extracted. When operating between 79 C. and 41 C. cyclohexane is extracted. Then cyclohexane may be separated from either or both of these materials as an extract phase and the l-heptene may likewise be separated from the ntion of methylcyclohexane reux in the separation of methylcyclohexane from admixture with n-heptane, this system is merely an example of the principle embodied in myI invention. My process may be used in the separation of other hydrocarbon from other mixtures with the simultaneous marked reduction in the heat requirement in the extract recovery still.

A solvent to be useful according to this invention must possess a melting point higher than the feed materials to be separated so that the solvent can crystallize in the chiller 31` with the `hydrocarbons present at this point remaining as liquid.

Materials of construction for the apparatus to be used may in general be selected from those commercially available, taking into account corrosive properties of any materials in the process.

While certain embodiments of the invention have been described for illustrative purposes, the invention is obviously not limited thereto.

I claim:

l. A solvent extraction operation comprising the steps of solvent extracting a liquid feed stock with a liquid selective solvent having a melting point higher than that of said feed stock to produce a raiiinate phase and an extract phase, separating these phases, cooling the separated extract phase to its selective solvent crystallizing temperature to produce crystals of solid selective solvent, a first liquid phase comprising a saturated solution of extract material in selective solvent and a second liquid phase comprising extract material, returning this second liquid phase to the extraction operation as extract phase reflux and recovering extract material from said rst liquid phase as a product of the process.

2. A process for separating methylcyclohexane from admixture with normal heptane comprising the steps of treating said admixture with phenol and water as a solvent under solvent extraction conditions to pro-duce a raffinate phase comprising normal heptane and an extract phase comprising phenol, water and rnethylcyclohexane, withdrawing said rainate phase as one product of the process, withdrawing said extract phase and cooling this phase to Such a temperature to form crystals of phenol, a rst liquid phase comprising aqueous phenol saturated with methylcyclohexane and a second liquid phase comprising methylcyclohexane, separating the so formed liquid phases from said crystals, separating the first and second liquid phases from one another, recovering methylcyclohexane from the separated first liquid phase as a second product of the process and returning the separated second liquid phase to the extraction operation at a point near the point of extract phase withdrawal as liquid reflux.

3. The process of claim 1 wherein the extractant is aqueous phenol.

4. The process of claim l wherein the extractant is an aqueous cresol.

5. The process of claim 4 wherein the cresol is orthocresol.

6. The process of claim 4 wherein the cresol is paracresol.

7. rIhe process of claim 1 wherein the extractant is 5 aqueous 2,3-dimethyl phenol.

8. The process of claim l wherein the extractant is aqueous levulinic acid.

9. A process for separating methylcyclohexane from admixture With normal heptane comprising the steps of contacting said admixture with water containing phenol under solvent extraction conditions in an extraction zone to produce a raffinate phase and an extract phase, removing the rainate phase from said zone, separating normal heptane from dissolved aqueous phenol of said rainate phase, recovering the separated normal heptane as one meltin'ghthe latter andreturningthe same to the. extractionl zone as aseoond portion of -extractang .from the two liquid` pliasjesnsieparating, a rst, liquid phase comprisingaqueous phenol s'aturated`with methylcyclohexane anda second liquid phasey coniprisingikmethylcyclohexane, from said rstliqtid phasey recovering methylcyclohexane as a second product of, the process, andA4 returningV theV aqueous,

phenol as. a further portionlkofthe, extractionsolventvto said extraction operation', and returninglsaid secondliquid phase comprising4` methylcyclohexane tothe extraction zone :atj ,a ypoint nearthe poi-ntoi'extract .phase withdrawal asreux'.

I0. The process of claim 9'wheren the extraction `operation, is carried out, at a. temperature within` the range of 70`"to15`0' F.'

11.1*11ieproess of; claims, whe'rein-1hemmbineareturnedJ solvent. contains fromS.` to; 15. per. cent by.` weight water.; v

12. 'IheprocesslofjclairnA Whereimtheextraction,operation is carried. out 4at a temperature, within vthe yrange Yof- 70?" toy 15.0,`FI and thecombinecllsolventcontains.,from` 5fto 15'per centwater by weight. Y

is cooled 'to a temperature ofSS?" to 40 Fl to precipitate said phenolecrystals,

R'ef'erenc'eszCited in ithele of L this' patent UN ITEDV' STATES,- PATENTS 

1. A SOLVENT EXTRACTION OPERATION COMPRISING THE STEPS OF SOLVENT EXTRACTING A LIQUID FEED STOCK WITH A LIQUID SELECTIVE SOLVENT HAVING A MELTING POINT HIGHER THAN THAT OF SAID FEED STOCK TO PRODUCE A RAFFINATE PHASE AND AN EXTRACT PHASE, SEPARATING THESE PHASES, COOLING THE SPARATED EXTRACT PHASE TO ITS SELECTIVE SOLVENT CRYSTALLIZING TEMPERATURE PHASE COMPRISING A SATURATED SOLUTION OF EXTRACT MATERIAL IN SELECTIVE SOLVENT AND A SECOND LIQUID PHASE COMPRISING EXTRACT MATERIAL, RETURNING THIS SECOND LIQUID PHASE TO THE EXTRACTION OPERATION AS EXTRACT PHASE REFLUX AND RECOVERING EXTRACT MATERIAL FROM SAID FIRST LIQUID PHASE AS A PRODUCT OF THE PROCESS. 